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117 lines
3.6 KiB
117 lines
3.6 KiB
/* oneit.c - tiny init replacement to launch a single child process.
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*
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* Copyright 2005, 2007 by Rob Landley <rob@landley.net>.
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USE_ONEIT(NEWTOY(oneit, "^<1nc:p3[!pn]", TOYFLAG_SBIN))
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config ONEIT
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bool "oneit"
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default y
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help
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usage: oneit [-prn3] [-c CONSOLE] [COMMAND...]
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Simple init program that runs a single supplied command line with a
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controlling tty (so CTRL-C can kill it).
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-c Which console device to use (/dev/console doesn't do CTRL-C, etc)
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-p Power off instead of rebooting when command exits
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-r Restart child when it exits
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-n No reboot, just relaunch command line
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-3 Write 32 bit PID of each exiting reparented process to fd 3 of child
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(Blocking writes, child must read to avoid eventual deadlock.)
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Spawns a single child process (because PID 1 has signals blocked)
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in its own session, reaps zombies until the child exits, then
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reboots the system (or powers off with -p, or restarts the child with -r).
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Responds to SIGUSR1 by halting the system, SIGUSR2 by powering off,
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and SIGTERM or SIGINT reboot.
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*/
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#define FOR_oneit
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#include "toys.h"
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#include <sys/reboot.h>
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GLOBALS(
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char *c;
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)
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// The minimum amount of work necessary to get ctrl-c and such to work is:
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//
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// - Fork a child (PID 1 is special: can't exit, has various signals blocked).
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// - Do a setsid() (so we have our own session).
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// - In the child, attach stdio to TT.c (/dev/console is special)
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// - Exec the rest of the command line.
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//
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// PID 1 then reaps zombies until the child process it spawned exits, at which
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// point it calls sync() and reboot(). I could stick a kill -1 in there.
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// Perform actions in response to signals. (Only root can send us signals.)
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static void oneit_signaled(int signal)
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{
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int action = RB_AUTOBOOT;
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toys.signal = signal;
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if (signal == SIGUSR1) action = RB_HALT_SYSTEM;
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if (signal == SIGUSR2) action = RB_POWER_OFF;
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// PID 1 can't call reboot() because it kills the task that calls it,
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// which causes the kernel to panic before the actual reboot happens.
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sync();
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if (getpid()!=1) _exit(127+signal);
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if (!vfork()) reboot(action);
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}
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void oneit_main(void)
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{
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int i, pid, pipes[] = {SIGUSR1, SIGUSR2, SIGTERM, SIGINT};
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// Setup signal handlers for signals of interest
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for (i = 0; i<ARRAY_LEN(pipes); i++) xsignal(pipes[i], oneit_signaled);
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if (FLAG(3)) {
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// Ensure next available filehandles are #3 and #4
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while (xopen_stdio("/", 0) < 3);
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close(3);
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close(4);
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xpipe(pipes);
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fcntl(4, F_SETFD, FD_CLOEXEC);
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}
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while (!toys.signal) {
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// Create a new child process.
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pid = XVFORK();
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if (pid) {
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// pid 1 reaps zombies until it gets its child, then halts system.
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// We ignore the return value of write (what would we do with it?)
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// but save it in a variable we never read to make fortify shut up.
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// (Real problem is if pid2 never reads, write() fills pipe and blocks.)
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while (pid != wait(&i)) if (FLAG(3)) i = write(4, &pid, 4);
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if (FLAG(n)) continue;
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oneit_signaled(FLAG(p) ? SIGUSR2 : SIGTERM);
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} else {
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// Redirect stdio to TT.c, with new session ID, so ctrl-c works.
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setsid();
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for (i=0; i<3; i++) {
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close(i);
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// Remember, O_CLOEXEC is backwards for xopen()
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xopen_stdio(TT.c ? : "/dev/tty0", O_RDWR|O_CLOEXEC);
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}
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// Can't xexec() here, we vforked so we don't want to error_exit().
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toy_exec(toys.optargs);
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execvp(*toys.optargs, toys.optargs);
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perror_msg("%s not in PATH=%s", *toys.optargs, getenv("PATH"));
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break;
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}
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}
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// Give reboot() time to kick in, or avoid rapid spinning if exec failed
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sleep(5);
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_exit(127);
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}
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